System and process for co-producing dimethyl carbonate and ethylene glycol

Abstract

A system and a process for co-producing dimethyl carbonate and ethylene glycol. The system comprises an interconnected ethylene carbonate preparation unit and an ethylene carbonate alcoholysis unit. The ethylene carbonate preparation unit comprises a fixed bed reactor and a light-component stripping column connected to each other. The fixed bed reactor is filled with a supported ionic liquid catalyst. The process comprises the steps of: reacting carbon dioxide and ethylene oxide as raw materials in the fixed bed reactor to produce ethylene carbonate, purifying the ethylene carbonate and then mixing it with an alcoholysis reaction catalyst, and reacting the mixture with methanol in a reactive distillation tower, producing dimethyl carbonate and ethylene glycol. The process increases the conversion rate of ethylene oxide and avoids the need for a process of separating conventional homogeneous catalysts from ethylene carbonate, thereby reducing process energy consumption and simplifying process procedures.

What is claimed is: 
     
       1. A system for co-producing dimethyl carbonate and ethylene glycol, comprising an ethylene carbonate preparation unit and an ethylene carbonate alcoholysis unit which are connected with each other;
 the ethylene carbonate preparation unit comprises a fixed bed reactor and a light-component removal tank which are connected with each other; and 
 the fixed bed reactor is filled with an immobilized ionic liquid catalyst. 
 
     
     
       2. The system according to  claim 1 , wherein the fixed bed reactor is provided with a heat removal device. 
     
     
       3. The system according to  claim 1 , wherein a top feed outlet of the light-component removal tank is connected to a carbon dioxide feed inlet of the fixed bed reactor. 
     
     
       4. The system according to  claim 1 , wherein a compressor is disposed on a pipeline between the top feed outlet of the light-component removal tank and the carbon dioxide feed inlet of the fixed bed reactor. 
     
     
       5. The system according to  claim 1 , wherein the ethylene carbonate alcoholysis unit comprises a reactive rectification column. 
     
     
       6. The system according to  claim 5 , wherein a bottom feed outlet of the light-component removal tank is connected to an ethylene carbonate feed inlet of the reactive rectification column, and an alcoholysis reaction catalyst feed inlet is disposed on a pipeline between the bottom feed outlet of the light-component removal tank and the ethylene carbonate feed inlet of the reactive rectification column;
 the ethylene carbonate feed inlet of the reactive rectification column is higher than a methanol feed inlet. 
 
     
     
       7. The system according to  claim 6 , further comprising a dimethyl carbonate refining unit connected with the ethylene carbonate alcoholysis unit. 
     
     
       8. The system according to  claim 7 , wherein the dimethyl carbonate refining unit comprises a high-pressure concentration column and a low-pressure refining column which are connected with each other. 
     
     
       9. The system according to  claim 8 , wherein a top feed outlet of the reactive rectification column is connected with a feed inlet of the high-pressure concentration column, and a bottom feed outlet of the high-pressure concentration column is connected to the feed inlet of the low-pressure refining column;
 a top feed outlet of the high-pressure concentration column is connected to the methanol feed inlet of the reactive rectification column; 
 a top feed outlet of the low-pressure refining column is connected to the feed inlet of the high-pressure concentration column. 
 
     
     
       10. The system according to  claim 6 , further comprising an ethylene glycol refining unit connected with the ethylene carbonate alcoholysis unit. 
     
     
       11. The system according to  claim 10 , wherein the ethylene glycol refining unit comprises an ethylene glycol light-component removal column, a hydrolysis reactor and an ethylene glycol refining column which are connected in sequence. 
     
     
       12. The system according to  claim 11 , wherein a bottom feed outlet of the reactive rectification column is connected to a feed inlet of the ethylene glycol light-component removal column, a bottom feed outlet of the ethylene glycol light-component removal column is connected to a feed inlet of the hydrolysis reactor, and a feed outlet of the hydrolysis reactor is connected to a feed inlet of the ethylene glycol refining column;
 a top feed outlet of the ethylene glycol refining column is connected to the methanol feed inlet of the reactive rectification column. 
 
     
     
       13. A process for co-producing dimethyl carbonate and ethylene glycol by using the system according to  claim 1 , comprising the following steps:
 (1) carbon dioxide and ethylene oxide as raw materials are introduced into the fixed bed reactor so that the two are contacted and reacted to generate ethylene carbonate, and the reaction product and unreacted raw materials are fed into the light-component removal tank for separation; and 
 (2) the ethylene carbonate is extracted from the bottom of the light-component removal tank, and mixed with an alcoholysis reaction catalyst, followed by reacting with methanol in a reactive rectification column to generate dimethyl carbonate and ethylene glycol. 
 
     
     
       14. The process according to  claim 13 , further comprising: the carbon dioxide extracted from the top of the light-component removal tank is pressurized by a compressor and then fed back to the fixed bed reactor. 
     
     
       15. The process according to  claim 14 , wherein the feeding molar ratio of carbon dioxide to ethylene oxide in step (1) is 1.2-10:1; the pressure within the fixed bed reactor is 1.5-6 MPa and the temperature is 80-200° C.; the pressure within the light-component removal tank is 1-100 kPa and the temperature is 50-200° C. 
     
     
       16. The process according to  claim 13 , wherein the alcoholysis reaction catalyst in step (2) is one selected from the group consisting of an alkali metal oxide, an alkali metal hydroxide, an alkali metal carbonate, an alkoxide, an ionic liquid, and a combination of at least two selected therefrom. 
     
     
       17. The process according to  claim 14 , wherein the feeding molar ratio of ethylene carbonate to the alcoholysis reaction catalyst is 100-1000:1;
 the feeding molar ratio of ethylene carbonate to methanol is 1:7-32; 
 the pressure within the reactive rectification column is 100-400 kPa, the temperature at the column top is 60-110° C., and the temperature at the column bottom is 80-130° C. 
 
     
     
       18. The process according to  claim 13 , further comprising a dimethyl carbonate purification step. 
     
     
       19. The process according to  claim 18 , wherein the dimethyl carbonate purification step comprises: an azeotrope of dimethyl carbonate and methanol is extracted from the top of the reactive rectification column, and fed into a high-pressure concentration column and a low-pressure refining column in sequence for separation; the methanol extracted from the top of the high-pressure concentration column is fed back to the reactive rectification column, and the mixture of dimethyl carbonate and methanol extracted from the top of the low-pressure refining column is fed back to the high-pressure concentration column, and dimethyl carbonate is extracted from the bottom of the low-pressure refining column. 
     
     
       20. The process according to  claim 19 , wherein the pressure within the high-pressure concentration column is 0.5-6 MPa, and the temperature at the column top is 10-150° C. higher than the temperature at the column bottom of the reactive rectification column;
 the concentration of the methanol extracted from the top of the high-pressure concentration column is 90-99.9 wt %; 
 the pressure within the low-pressure refining column is 0.1-1 MPa. 
 
     
     
       21. The process according to  claim 13 , further comprising an ethylene glycol purification step. 
     
     
       22. The process according to  claim 21 , wherein the ethylene glycol purification step comprises: a mixture of ethylene glycol, methanol, ethylene carbonate and the alcoholysis reaction catalyst is extracted from the bottom of the reactive rectification column, and fed into an ethylene glycol light-component removal column, a hydrolysis reactor and an ethylene glycol refining column in sequence for separation, hydrolysis and refinement, and the methanol extracted from the top of the ethylene glycol light-component removal column is fed back to the reactive rectification column, and ethylene glycol is extracted from the side line of the ethylene glycol refining column. 
     
     
       23. The process according to  claim 22 , wherein the pressure within the ethylene glycol light-component removal column is 1-80 kPa and the operating temperature is 20-180° C.;
 the pressure within the hydrolysis reactor is 110-900 kPa and the operating temperature is 50-180° C.; 
 the pressure within the ethylene glycol refining column is 1-80 kPa and the operating temperature is 35-190° C.